What are the ways by which Allah communicates with humans,

All perfect praise be to Allaah, The Lord of the Worlds.  I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

Allaah The Almighty created mankind to worship Him, and He legislated laws and clarified to them, through the teachings of His Messengers. Allaah made the implementation of these laws a means to get close to Him. For example, Allaah revealed to His Messengers books that make His slaves know about Him and He sealed His books and laws with the Message of the Prophet Muhammad .

Allaah clarified to His slaves that the happy and successful person is the one who follows Allaah's Sharee'ah [legislation] and the miserable is the one who rejects this Sharee'ah.

Therefore, this is the way Allaah communicates with His creation, He clarifies to them His Sharee'ah through the teachings and preaching of His Messengers, may Allaah exalt their mention, and His slaves get closer to Him through doing what He legislated for them.

As regards to the method of His revelation to the Messengers, then among the ways of revelation is that an angel descends with what Allaah wants to convey to His Prophet, who, in turn, would convey it to his nation. Also, among the other ways is to inspire to the heart of the Prophet, or to speak to him directly but from behind a screen; Allaah Says (what means): {And it is not for any human being that Allaah should speak to him except by revelation or from behind a partition or that He sends a messenger [i.e. angel] to reveal, by His permission, what He wills. Indeed, He is Most High and Wise.}[Quran 42:51]

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Allaah Knows best.